The present invention relates to a hydrogen storage material comprising particles of a hydrogen storage alloy and a method for manufacturing the same. The present invention is also directed to an electrode of a hydrogen storage alloy for use in negative electrodes of nickel-metal hydride storage batteries as a specific application of the hydrogen storage material and a method for manufacturing the electrode.
Recently, there is a wide application of hydrogen storage alloys which can absorb therein and desorb therefrom hydrogen in a reversible manner. For example, it becomes possible to reserve or convey hydrogen safely in an ordinary vessel if only a hydrogen storage alloy material is included in the vessel. Since hydrogen storage alloys allow selective absorption and desorption of hydrogen, they can also be used for refining hydrogen. Their other application includes a converter for a variety of energy by utilizing exothermic and endothermic reactions of the hydrogen storage alloys during their hydrogen absorption and desorption. They can also be applied as electrode materials for the clean nickel-metal hydride storage batteries affording a high energy density which should be replaced with conventional nickel-cadmium storage batteries. Those nickel metal-hydride storage batteries have been utilized as the power sources for a variety of portable electronic equipment, electric vehicles, etc.
The hydrogen storage alloy is in nature collapsed and pulverized into fine particles when it is forced to absorb therein and desorb therefrom hydrogen repeatedly. The hydrogen storage alloy, therefore, has a drawback that when it is used for storing, conveying or refining hydrogen, those pulverized particles become fugacious out of the alloy together with hydrogen gas, reducing the amount of reserved hydrogen or clogging a filter included in a refining device. The use of this hydrogen storage alloy for electrode has a drawback that pulverization of the alloy into fine particles will take place if charge and discharge operations are repeated for an electrode including such alloy, which in turn causes the pulverized particles to fall off from the surface of an electrode substrate, thereby decreasing the discharge capacity of a battery using the electrode, resulting in impaired life of the battery. The hydrogen storage alloy is disadvantageously poor in thermal conductivity, which restricts its use as an energy converter.
Proposed methods for solving these problems include: 1) to add a resin binder to hydrogen storage alloy particles and pressure-mold the resultant mixture to a hydrogen storage alloy material or 2) to plate particles of a hydrogen storage alloy with a metal film and subsequently pressure-mold the plated alloy particles into a hydrogen storage alloy material. In the former method, the binding force between the particles can be enhanced by increasing the amount of a binder, but this disadvantageously decreases the amount of hydrogen storage per unit weight of the alloy. In the latter method, although it depends on the kind of metal used for plating, the resultant alloy material is insufficient in strength despite strong to a certain degree.